(1) Field of Invention
The invention relates to a method for producing a bulk material of agglomerates having rubber particles and wax, especially in the form of pellets. Furthermore the invention relates to the composition of agglomerate produced with this process, particularly in form of a pellet, and the use of this bulk material for the production of asphalt or of a mixed material with a bituminous material or of a bituminous material having improved properties.
(2) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
It is well known that these asphalts can be modified with various additives to improve the performance and durability in road construction, for example, to prevent distortions such as ruts and to simultaneously prevent cracking from exposure to cold or mechanical fatigue. For example, elastomers (e.g. SBS and SBR), plastomers (e.g., EVA and PE) or rubber particles from tire recycling are used as additives. In addition, a second group of additives is in use, which are classified as waxes, e.g. Fischer-Tropsch paraffins, peat waxes and amide waxes. These additives also improve the resistance against deformation, but show only little or no improvement in fatigue and low temperature properties of the asphalt due to the lack of an elastic component. An important effect of the wax additives is the reduction of the viscosity of the bitumen and the asphalt mixture at the production and processing temperatures. This allows a simplification of the production of the asphalt mixture and the asphalt layers and a reduction of the production and processing temperature. This results in energy savings and reduced environmental impact.
Basically, the additives are homogeneously mixed into the binder bitumen before the asphalt is produced or are added directly during the production of the asphalts.
The modification with rubber occurs either in a wet process or in a dry process. In a wet process, approximately 5-20% rubber particles are introduced into hot (160-200° C.) bitumen and stirred for 1-4 hours. Only a small portion of the rubber goes into solution, while the rest swells by absorbing oil components of the bitumen. The resulting mixture remains homogeneous and requires continuous stirring until the asphalt is produced to prevent the rubber particles from settling. The viscosity of the bitumen is greatly increased by the rubber and changes with storage time due to swelling and depolymerization processes, as described by Diedrich in his article “The use of modified scrap rubber powder in North American road surfaces”, Asphalt 5/2000, 6-10.
In the dry process, the rubber particles are added directly into the asphalt mixer and mixed with bitumen and minerals. Disadvantageously, the mixing time must be increased for attaining a homogeneous distribution. Even when the mixing time is increased, the time for interaction with the bitumen is too short to achieve swelling and dissolution comparable with the wet process. There is a risk that the desired thick binder films and a high bonding strength of the binder cannot be achieved. Therefore, the quality of the rubber-modified asphalt produced with the dry process is generally lower.
To avoid the disadvantages of the dry process, a master batch can also be produced from rubber particles and bitumen, which is produced in granular form, as realized, for example, in the so-called Tecroad product.
Specifically, experts have repeatedly tried to suggest improvements in the use of rubber for asphalts.
It is known from EP 1 873 212 B1 to modify rubber powder by swelling with 2-40% aromatic oils and to subsequently modify bitumen in a wet process, wherein the pre-swelling reduces the temperature and the mixing time in the bitumen modification. Disadvantageously, however,                the swollen rubber powders are not necessarily viscosity-reducing,        the resistance against deformation is reduced at ambient temperatures,        there is no compatibility of rubber and bitumen,        aromatic oils that are harmful to health and the environment are used,        the product is in a form that cannot be easily and safely stored, transported and dispensed with systems that typically exist in asphalt mixing plants (pneumatic conveying, screw conveying),        the product is unsuitable for direct addition into the asphalt mixer which increases the complexity (time, energy, investment for a modifying plant) for the previous bitumen modification, and        due to the risk of dust explosions, such additives can only be delivered in this way as a fine powder by complying with costly requirements.        
Furthermore, a granulate including rubber, a process for its production, and process for producing an asphalt mixture using the granulate are known from WO/1997/026299 and DE 196 01 285 A1.
Accordingly, a free-flowing granulate of 50-95% rubber and bitumen or polymer plastic (thermoplastic elastomers or plastomers) is described, whose constituents are evenly distributed at temperatures >130° C. under exposure to shear forces. Up to 25% additives may be present (sulfur, vulcanization accelerators, heavy oil, fatty acids, cellulose fibers). The granulate may be prepared from a mass that is homogenized or chemically combined at a high temperature in a kneader or by pressing the individual components at a low temperature (edge mill, orifice plate). This allows the manufacture of rubber asphalt mixture for road surfaces by adding the granulate in the asphalt mixing process to the minerals or to the bitumen.
The disadvantages which operate against a reduction of the viscosity and allow emissions and deformations are here also overwhelming. In addition, oily constituents may be removed from the bitumen, which may cause hardening of the bitumen.
When the skilled person proceeds according to the method for the production of hydrated lime pellets for use in asphalt production and/or soil conditioning by pelleting the hydrated lime and a binder (at 0.5 to 69%) according to the U.S. 2008/0216712 A1, he would notice that hydrated lime improves the water resistance of asphalt and the adhesion of the binder to the minerals and that rubber and wax in this paper act as a binder.
The binder may here be water-based or hydrophobic and may include at least one of the following components: bitumen, plastomers, elastomers, rubber, ground tire rubber, pre-reacted ground tire rubber. The pellet may contain up to 30% of an additive (aliphatic mineral oil distillate, plastomers, elastomers, rubber, pre-reacted rubber tires). It may also contain as an additional component: rheology modifiers, structural additives, solvents, dyes.
Oils and waxes are mentioned as suitable organic binders for the pellet, and the pellet may in one embodiment be made of a core of hydrated lime and a shell composed of the binder, wherein the shell may in turn be made of bitumen and high-temperature waxes.
The expert finds no evidence in this analysis that would lead to a reduced viscosity and an improved resistance against deformation. Instead, he must conclude that oily constituents can here also disadvantageously be removed from the bitumen.
Furthermore, WO 94/14896 and CA 2,152,774 disclose a method for preparing a bituminous composition. Rubber particles from scrap tires are here swollen by heating and shearing in a highly aromatic hydrocarbon oil and at least partially depolymerized. This material is dispersed in bitumen and a compatibilizer (liquid rubber), and, if necessary, a crosslinking agent may be added in order to obtain a storage-stable binder. So-called masterbatches with 25-80% dispersed, stabilized rubber in bitumen are produced, which is formed into a pellet with fillers and polymers.
No advantages for a reliable compaction, energy savings, reduced emissions and resistance against deformation can be found. Disadvantageously, aromatic oils which are harmful to health/environment are even used.
The patent DE 601 21 318 T2 relates to a method for producing a granular rubber material and its use in bitumen, and discloses the production of rubber granules, e.g. from scrap tires, and a thermal adhesive (polyolefins, PE, PP, EVA) with optional addition of fibers in an extrusion process. The heat generated by friction of 80-300° C. is intended to melt the hot melt glue.
Polyolefins cause an increase in the viscosity of asphalt. There is still a risk that oily components are removed from the bitumen, causing hardening of the bitumen.
In a process for preparing bituminous mix disclosed in the patent DE 44 30 819 C1, in particular road asphalt, with the addition of rubber and activated carbon, the activated carbon reduces vapor/gaseous emissions in the production of hot asphalt and elution of harmful substances due to water in cold asphalt produced with tar-containing recycled asphalt. Rubber is here added to the hot mineral prior to the bitumen together with or separately from the activated carbon or previously mixed with the bitumen. However, viscosity-reducing effects and an increased resistance against deformation are not taught.
In a mastic asphalt according to CH 694 430 A5, through addition of rubber granulate, preferably from scrap tires, the lower density of the rubber granulate in comparison to the mastic asphalt is surmised to cause an accumulation on the surface of the asphalt layer in order to produce a more elastic surface, noise abatement, improved antiskid properties. The expert repeatedly fails to find suggestions for reducing the viscosity, increasing the resistance against deformation, simplifying storage and transport, improving dispensing and preventing hardening of the bitumen.
The following publications also fail to disclose aspects that would obviate the previously analyzed disadvantages:                JP 2004060390 A discloses an asphalt with a 2-component epoxy resin, wherein the main component of the epoxy resin is added to the asphalt mixture and the hardener is incorporated in the form of a swelling agent absorbed in rubber particles,        JP 2008050841 A, wherein a lattice bottom plate protects the “paved surface” and reduces noise and improves the grip and wherein the plate is produced from scrap rubber tires and polyethylene,        JP 10338812 A with a water-swellable composition and “water stop material” consisting of water-swellable clay, bitumen, temperature-sensitive enhancers, including rubber and reinforcing fillers        DE 42 32 907 A1 discloses water-swellable products, which are however resistant against water and many chemicals for the manufacture of seals with solid or cellular structure, wherein a bitumen emulsion is also used as a reactant in lieu of water for modifying the product properties and wherein e.g. rubber powder can be added as an inexpensive filler; however, there is no reference to asphalt, and        DE 24 08 690 C2 discloses thermoplastic materials produced by mixing rubber material pieces, for example from scrap tires, and a thermoplastic binders, such as PE, EVA, SBS.        
Lastly, the U.S. 2010/0056669 A1 discloses producing a storage-stable pellet for asphalt production, which is composed of                a core composed of 15-30% ground tire rubber and 70-85% road construction bitumen, and        a shell coating the core, so that the pellet has a maximum size of 1/16 to 2 inches, composed of a water-resistant polymer or wax, or fine particles.        
The aforementioned core contains less than 10 wt.-% sulfur; the fine particles are hydrated lime (or ground asphalt [Claim 4]) making up less than 40 wt.-% of the whole pellet.
The pellet may also contain rock powder, additional bituminous binders, non-bituminous binders, structural additives, dyes, salts, viscosity modifiers.
Materials with non-Newtonian behavior are mentioned, e.g. polysaccharides. It can thus be concluded that this does not include viscosity reducers.
The process for preparing these pellets includes procurement of ground tire rubber and road construction bitumen, reacting rubber and bitumen for at least 45 minutes, combining the reaction mixture with fine particles to form the core, and coating the core with a shell to form the pellet.
The method for producing asphalt includes the liquefaction of the pellets by heating and combining with minerals, and optionally the addition of additional bitumen.
The material for the so-called shell is supposed to include, inter alia, crude oil wax, Sasol Wax and Sasobit, and also Sasol Wax as a component of the binder for the so-called core beside bitumen and rubber, because Sasol Wax is known to be useful for reducing the temperatures for the preparation and discharge of asphalt from about 325-300° F. (162-150° C.) to 280-250° F. (139-121° C.).
The above-mentioned reactions of rubber- and bitumen should be performed at high temperatures of 350-380° F. (about 175-195° C.).
A skilled artisan will deduce from U.S. 2010/0056669 A1 that already                a pre-reaction of the rubber can occur (by mixing with hot bitumen), and        the addition of wax to reduce the temperatures for producing and applying asphalt has proven successful.        
After thorough analytical investigation, however, the skilled artisan will recognize that these so-called pellets do not represent an additive for modifying asphalt into rubber asphalt, but rather a kind of binder for producing pelleted asphalt which represents the binder of the asphalt exclusively or with limited additional fractions of bitumen, which leads to disadvantages. Current storage systems, conveyor systems and metering systems of asphalt mixing plants are not constructed for the use of a solid, granular binder.
The skilled artisan expert may infer herefrom a teaching of bitumen hardening, but not in conjunction with integrated swelling.
Even when also consulting the WO 2010/023173 A1, no approaches for solving the following task are found in the combination of the analyzed prior art sources.
The last-mentioned publication discloses a bituminous composition of a “wet process”. Disadvantageously, a rubber-modified finished binder is used, and the user at the asphalt mixing plant needs an additional binder tank for storage, which is usually not available. There is also a lack in flexibility for adjustment, since only one binder with a defined rubber concentration and a defined hardness class is contained in the tank. As a further disadvantage, time, energy and a modification facility are required for the production of the bituminous composition. Moreover, the swelling of the rubber does not prevented hardening of the bitumen by removing oily components from the bitumen. The viscosity of the bituminous composition remains the same as in a conventional rubber-modified bitumen, and is not reduced.